The present invention relates to an automatic molding machine, which is capable of molding resin-mold type semiconductor devices with release film.
Conventionally, automatic transfer molding machines have been used so as to manufacture the resin-mold type semiconductor devices, e.g., PLCC, QFP. In the conventional automatic molding machine, molding dies, which include cavities, are set in a press mechanism, and work pieces and resin tablets are automatically set in the molding dies, then the work pieces are molded with the resin.
In the case of molding lead frames, which are formed into rectangular strips, as the work pieces, a magazine in which a plurality of lead frames have been accommodated is set in the molding machine, and the lead frames are automatically fed onto the molding dies, then they are molded with the resin. After the molding, the molded products are taken out from the molding dies, and disused resin is removed, then the products are accommodated in a tray, etc.
In the conventional molding machine, the melted resin directly contacts inner faces of the molding sections of the molding dies and solidifies in the molding dies. So, the ejector pins are provided in the molding dies. The ejector pins eject the molded products from the molding dies when the molding dies are opened.
These days, semiconductor elements of the semiconductor devices have unique high-frequency characteristics and their consumption of electricity is very great, so the resin-mold type semiconductor devices must be manufactured on the basis of said characteristics, etc. In the resin-mold type semiconductor devices, the resin affects said characteristics, etc. of the semiconductor elements, so selection of the resin is a very important factor.
In the case of employing the semiconductor element whose calorific value is great, for example, the resin having high thermal conductivity, e.g., the resin including heat-resisting ceramic fillers: alumina, etc. whose thermal conductivity is high, is used. However, the resin including the ceramic fillers abrades the molding dies. So gates of the molding dies are rapidly abraded, and finally the molding dies cannot be used.
And, these days thin semiconductor devices are required. But, in the case of molding the semiconductor device having a thin package section, it is very difficult to fill the resin in the cavity spaces, so that voids and non-filled parts are formed in the molded package section. With a small package section, pitch of the wire bonding sections of the lead frame is very narrow, so electric wires are swept by the resin flow passing therethrough. To avoid the wire sweep, the resin having high fluidity is used, but the resin having high fluidity is apt to invade into sliding parts of the ejector pins and a plunger. By the resin invasion, the sliding parts cannot move, and the melted resin which leaks on the parting faces of the molding dies makes the molding dies and the molded products dirty.
To solve the above described disadvantages of the conventional automatic molding machine, a molding method using release film has been invented. In this method, heat-resisting soft film, which is capable of easily peeling off from the solidified resin, is used as release film. Inner faces of the molding sections, e.g., the cavities, of the molding dies are covered with the release film, so that the resin is capable of molding without direct contact with the faces of the molding dies.
The molding method using the release film is shown in FIG. 15. On the left side of a center line L, a state of not filling the resin in the cavity space is shown; on the right side of the center line L, a state of filling the resin in the cavity space is shown. A work piece 204 is clamped by an upper die 200 and a lower die 202, which are the molding dies. Resin 208 is introduced from a pot 206 to the cavity space 210 to mold the work piece 204. Two sheet of the release film 212a and 212b are spread along inner faces of the cavities, etc., and they cover over the parting faces of the upper die 200 and the lower die 202. In this state, the melted resin is filled in the cavity space 210.
Note that, in this method, wrapped resin 150, in which the resin for molding is tightly wrapped with heat-resisting wrapping film which also acts as the release film, is used as the resin for molding the work piece 204. A perspective view of the wrapped resin 150 is shown in FIG. 16. The wrapped resin 150 is tightly wrapped with upper film and lower film. Edges of the upper film and the lower film are mutually sealed to form the wrapping film 151. The wrapped resin 150 is supplied into the pot 206 in a wrapped state to melt. Sealed parts of the wrapping film 151 are partially opened when a plunger 206a exerts pressure on the melted resin 208. Since the sealed edges of the wrapping film 151 are partially opened as a resin path, the melted resin 208 can be introduced into the cavity space 210 from the pot 206.
In the case of the molding method using the release film, the resin does not directly contact the faces of the molding dies, so the abrasion in the gates, the cavities, etc. of the molding dies can be prevented. Thus, any types of the resin can be used in the molding dies. And, the release film exists between the molding dies and the molded products, so the molded products can be easily ejected from the molding dies. Thus, structures of the molding dies can be simpler because no ejector pins are required therein. Since the faces of the molding dies are covered with the release film, no resin invades into small gaps in the molding dies even if the resin has high fluidity.
In the method using the release film, any types of resin can be employed, so the most proper resin can be selected according to characteristics, etc. of products.